For walks around town I love to use a 6x6 folder. I have an Ansco Titan that fits in my back pocket like an over-stuffed wallet. When I need more than guestimation focusing I use a Rolleiflex or Hassy 500cm.

Another 6x6 SLR that I've had lot's of fun with, but is sort of under the radar, is the Graflex Norita (and previous incarnations). It's a lot like a Pentax 6x7, but it's 6x6. The story I heard about it (I don't know how good my sources are) is that it was designed by the guy who designed the Nikon F. The really cool thing about it is the standard 80mm f/2 lens it usually comes with.

The DoF markings on lenses can lead you astray. Basically, of course, only one distance is perfectly focussed at any time. Distances near that are nearly in focus, and it gets less focussed at closer and further distances. How unfocussed is "too unfocussed" to be acceptable? The DoF marks on lenses are based on a degree of "good enough" that can be very disappointing, depending on the subject.

I generally try to use the DoF marks on the lens for an aperture 2 stops wider than I'm actually using. This leads to "less" DoF, but at a quality of focus that justifies the use of a 120 size camera. If the subject does not "fit" the DoF limits, then I need to do more thinking about what to sacrifice in focus and still get the shot (or consider a tripod and a lower shutter speed).

If you need heaps of DoF, then consider 35mm. They are quite good, you know!